Backup overview

iCloud automatically backs up the most important data on your iOS 5 device. Once you have enabled Backup on your iPhone, iPad, or iPod touch in Settings > iCloud > Backup & Storage, it will run on a daily basis as long as your device:

is connected to Internet over Wi-Fi

is connected to a power source

has the screen locked

You can also back up manually whenever your device is connected to Internet over Wi-Fi by choosing Back Up Nowfrom Settings > iCloud > Storage & Backup.

What is backed up

You get unlimited free storage for:

Purchased music, movies, TV shows, apps, and books

Notes: Backup of purchased music is not available in all countries. Backups of purchased movies and TV shows are U.S. only. Previous purchases may not be restored if they are no longer in the iTunes Store, App Store, or iBookstore.

Some previously purchased movies may not be available in iTunes in the Cloud. These movies will indicate that they are not available in iTunes in the Cloud on their product details page in the iTunes Store. Previous purchases may be unavailable if they have been refunded or are no longer available in the iTunes Store, App Store, or iBookstore.
You get 5GB of free iCloud storage for:

You can select which applications back up their data and see how much storage space each application is using:

On your Home Screen, tap Settings

Tap iCloud

Tap Storage & Backup

Tap Manage Storage

Select the device you want to manage

If you need more iCloud storage, you can purchase additional iCloud storage from your iOS device, Mac, or PC.

The following items are not backed up to iCloud. You can sync these items with a computer using iTunes:

Music, movies and TV shows not purchased from the iTunes Store

Podcasts and audio books

Photos that were originally synced from your computer

Optimize iCloud On iPhone, iPad, iPod

1. Go to Settings and select iCloud. You’ll see some apps here, but notice these are only the pre-installed Apple apps! We want to find all the apps.
2. Scroll down to Storage & Backup, and tap it.
3. Choose the third choice shown, Manage Storage.
4. Select the entry for your iPhone under Backups.
5. Here, you’ll see a list of the top five storage-using apps. Scroll down and click Show All, and then select, app by app, which items you want to back up.
6. Decide which of your apps you don’t want to back up; toggle those to “off.” A red button reading “Turn Off & Delete” will appear.

If you click it, you’ll still have the app and its data locally on your iPhone; you’re just “deleting” its data from iCloud’s backup.
At the bottom of the screen, you’ll see how much space you have available. If you can clean up your app backup, you should be able to better optimize that free 5GB.